Toward the bioleaching of bauxite residue by Gluconobacter oxydans.

Aim: This project evaluated a biologically mediated strategy to solubilize several rare earth elements and critical raw materials, including scandium, from bauxite residue. This work seeks to expand on previous research on contact leaching with bauxite.

Methods and results: In this study, Gluconobacter oxydans was shown to secrete mixed organic acids, including gluconic acid, which was superior to pure gluconic acid in the dissolution of bauxite residue, even at low molarities. In situ contact leaching with G. oxydans significantly promoted the dissolution yield (recovery of metal present in the ore) of yttrium, aluminum, calcium, and titanium (41.18%, 67.79%, 80.16%, and 59.41%, respectively) but allowed for only marginal dissolution yield of scandium, lanthanum, cerium, and neodymium (13.40%, 14.74%, 24.41%, and 10.67%, respectively) at relatively low pulp densities. In addition, the dissolution yields of rare earth elements were reduced further with time, presumably as the oxides of these elements fell out of solution.

Conclusion: This work builds on previous research that seeks to extract rare earth elements and critical raw materials from bauxite residue through contact leaching with organic acids. Some elements such as yttrium, aluminum, calcium, and titanium could be effectively solubilized; however some elements showed reduced solubility, possibly due to tight association with the iron phase of the residue. However, the relative ease and speed of leaching, and improved solubilization, suggest that this could be a viable method for securing critical raw material supplies.